When separating the yolk from the white, use fresh cold eggs.
The yolk of fresh eggs will be round and compact - as an egg ages, the yolk absorbs liquid from the egg white and flattens out.. If you kept an egg long enough, the yolk and white would eventually merge into one.
A blood spot on the yolk is caused when a blood vessel on the yolk ruptures during the egg's formation. It actually indicates a fresh egg, since as the egg ages, water moves from the albumen (the egg white) into the yolk, diluting the blood spot. It is not a sign that the egg is fertile.
Egg yolks are one of the few foods that naturally contain Vitamin D.
One large egg yolk contains more than 2/3 of the daily limit of cholesterol recommended by the American Heart Association.
Use a plastic bottle to quickly separate an egg yolk from the white. This short video (1m 43s) is in Mandarin, but simply watching it tells the whole story.
QUESTION Dear Chef James, Today I baked cookies that required me to use hard boiled egg yokes instead of raw eggs. The Recipe is for ‘Neros Ears’ and comes from The ‘French Cookie Book’ by Bruce Healy Ingredients are butter, flour, confection sugar, 3 large hard boiled eggs, vanilla extract, glaze is one whole egg. The cookies are delicious What would the purpose of a hard boiled egg yoke do in a recipe. I Look forward to your response. Tanya
ANSWER Hello Tanya,
About Egg Yolks in General: Egg yolks contain a lot of fat (about 10-12 grams per yolk), so one reason to use egg yolks is for the fat, another is for the color. Egg yolks also tend to make a moister and more flavorful product. Finally, egg yolks also act as an emulsifier, helping to bind the ingredients together - a less crumbly cookie.
About Cooked Yolks: As for hard boiled - this has to do with the final texture and richness (mouth feel) of the cookies and how raw yolks would cook in the high heat of the oven. Raw yolks would bind the ingredients more than the cooked yolks, so the texture will be very different with the cooked yolks compared to raw yolks.
Raw egg yolks would produce a significantly different cookie. Try making a small batch with raw egg yolks to see how much difference it makes.